I have the i7-990x and if you want to overclock that then you have to disable HyperThreading in the BIOS.

Just running it in idle with no overclock the difference in core temps is between three and four degrees Celsius lower with HT disabled.

Having said that I am a fish out of water on this section of the forum because I have not yet felt the need to overclock my system. I have no interest in doing it just for the sake of it. It is however nice to have that ability should I ever have my system succumb to a CPU bottleneck.

I'm still rocking an air cooled i7 920, OC'd to the standard 3.7GHz. It still does a pretty good job in 90% of the high end AAA titles; only falling short in the open world games, like Saints Row 4, and the like. I'll probably keep the CPU until it fries itself, because the R9 290X I paired with it has really helped the games (and CPU have some legs).